On the Uplink Capacity of Hybrid Cellular Ad Hoc Networks

Towards increasing spatial reuse, cellular networks may be augmented with ad hoc connectivity. In the resulting hybrid network, the coverage area of the base station (BS) is reduced and the users within this area relay packets from/to the users outside. With this approach, shorter range, higher-rate links are used; this favors an increase in spatial reuse and thus, the achievable capacity. However, multi-hop relaying overhead can hurt capacity. In this paper, we analytically compute the uplink capacity, defined as an upper bound on the achievable throughput under max-min fairness. To gage the tightness of the bound, we seek to find the optimal transmission schedule for delivering the packets from the nodes in a cell to the BS. In general, constructing the optimal uplink schedule is NP-hard. We develop a heuristic approach and show via simulations that the resulting performance is close to the derived capacity bound. Our results suggest that (a) the hybrid network can achieve up to a 200 % increase in the uplink capacity compared to a pure cellular network, and (b) the simulated throughput is close to the analytically computed capacity showing that our bound is tight.